Let's say you've a symmetric encryption key. To backup the key and achieve split knowledge, you export the key as separate components.
If the key is a 128-bit key, you should get key components which are each 128-bits in length. You can have two or more components. These components can be XOR'd together (a bitwise operation) to recreate the initial encryption key.
These key components should be under the responsibility of different individuals (i.e. key custodians).
With the above, you have split knowledge - no single individual knows the full key and knowledge of a single component provides no means to derive the original key.
You also have dual control - at least two individuals are required in order to recreate the encryption key.
The key store relates to where the key is located - e.g. the data encryption key is likely stored as a cryptogram encrypted with a key encryption key of equal or greater strength.
Verification is typically through review of a documented process, interviews with key custodians, review of logs of key generation and component storage locations.